package com.xxbb.springbootapi.utils;

public class SnowFlake {


    /**

     * 起始的时间戳

     */

    private final static long START_STAMP = 1480166465631L;


    /**

     * 每一部分占用的位数

     */

    private final static long SEQUENCE_BIT = 12; //序列号占用的位数

    private final static long MACHINE_BIT = 5;   //机器标识占用的位数

    private final static long DATA_CENTER_BIT = 5;//数据中心占用的位数


    /**

     * 每一部分的最大值

     */

    private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);

    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);

    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);


    /**

     * 每一部分向左的位移

     */

    private final static long MACHINE_LEFT = SEQUENCE_BIT;

    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;


    private long dataCenterId;  //数据中心

    private long machineId;     //机器标识

    private long sequence = 0L; //序列号

    private long lastStamp = -1L;//上一次时间戳


    public SnowFlake(long dataCenterId, long machineId) {

        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0) {

            throw new IllegalArgumentException("dataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0");

        }

        if (machineId > MAX_MACHINE_NUM || machineId < 0) {

            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");

        }

        this.dataCenterId = dataCenterId;

        this.machineId = machineId;

    }


    /**

     * 产生下一个ID

     *

     * @return

     */

    public synchronized long nextId() {

        long currStamp = getNewStamp();

        if (currStamp < lastStamp) {

            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");

        }


        if (currStamp == lastStamp) {

            //相同毫秒内，序列号自增

            sequence = (sequence + 1) & MAX_SEQUENCE;

            //同一毫秒的序列数已经达到最大

            if (sequence == 0L) {

                currStamp = getNextMill();

            }

        } else {

            //不同毫秒内，序列号置为0

            sequence = 0L;

        }


        lastStamp = currStamp;


        return (currStamp - START_STAMP) << TIMESTAMP_LEFT //时间戳部分

                | dataCenterId << DATA_CENTER_LEFT       //数据中心部分

                | machineId << MACHINE_LEFT             //机器标识部分

                | sequence;                             //序列号部分

    }


    private long getNextMill() {

        long mill = getNewStamp();

        while (mill <= lastStamp) {

            mill = getNewStamp();

        }

        return mill;

    }


    private long getNewStamp() {

        return System.currentTimeMillis();

    }


    public static void main(String[] args) {

        SnowFlake snowFlake = new SnowFlake(2, 3);

        long start = System.currentTimeMillis();

        for (int i = 0; i < 1000000; i++) {

            System.out.println("当前生成的有序数字串："+snowFlake.nextId());

        }


        System.out.println("总共耗时："+(System.currentTimeMillis() - start));

    }

}